<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Document</title>
  <style>
    .a[data-v-1]{
      color:red;
      background-color: skyblue;
    }

    .a{
      color:blue;
      font-size: 30px;
    }
  </style>
</head>
<body>
  <div class="a" data-v-1>
    ABC
  </div>
</body>
</html>